1. Field of the Invention
The present invention relates to a plasma display apparatus and a driving method thereof, and more particularly, a plasma display apparatus that is capable of improving contrast and driving margin by enhancing a driving waveform supplied in a reset period of each subfield, and a driving method thereof.
2. Description of the Background Art
Generally, a plasma display panel (PDP) radiates a phosphorus by an ultraviolet with a wavelength of 147 nm generated during a discharge of He+Xe or Ne+Xe gas to thereby display a picture including characters and graphics.
FIG. 1 is a perspective view showing a structure of a conventional three-electrode AC surface plasma display panel. As shown therein, the three-electrode AC surface-discharge PDP includes a scan electrode 11(hereinafter, ‘Y electrode’) and a sustaining electrode 12(hereinafter, ‘Z electrode’) formed on an upper substrate 10, and an address electrode 22(hereinafter, ‘X electrode) formed on a lower substrate 20. The Y electrode 11 and the Z electrode 12 are formed from transparent electrodes, e.g., indium-tin-oxide (ITO), 11a and 12a, respectively. Bus electrodes 11b and 12b are formed on the Y electrode 11 and the Z electrode 12, respectively, so as to reduce resistance. On the upper substrate 10 provided with the Y electrode 11 and the Z electrode 12, an upper dielectric layer 13a and a protective film 14 are disposed. Wall charges generated upon plasma discharge are accumulated in the upper dielectric layer 13a. The protective film 14 protects the upper dielectric layer 13a from a sputtering generated during the plasma discharge and improves the emission efficiency of secondary electrons. This protective film 14 is usually made from MgO.
A lower dielectric layer 13b and barrier ribs 21 are formed on the lower substrate 20 provided with the X electrode 22. A phosphorus layer 23 is coated on the surfaces of the lower dielectric layer 13b and the barrier ribs 21. The X address electrode 22 is formed in a direction crossing the X electrode 11 and the Z electrode 12. The barrier ribs 21 are formed in parallel to the X electrode 22 to prevent an ultraviolet ray and a visible light generated by the discharge from being leaked into the adjacent discharge cells. The phosphorus layer 23 is excited and radiated by an ultraviolet ray generated upon plasma discharge to produce a red, green or blue color visible light ray. An inactive mixture gas, such as He+Xe or Ne+Xe, for a gas discharge is injected into a discharge space defined between the upper/lower substrate 10 and 20 and the barrier ribs 21. A driving waveform according to a driving method of a conventional plasma display panel having such a structure will be described as shown in FIG. 2.
FIG. 2 is a view showing a driving waveform according to a driving method of a conventional plasma display panel. As shown in FIG. 2, the plasma display panel is divided into a reset period for initializing, the full fields, an address period for selecting a cell to be discharged, a sustain period for sustaining a discharge of the selected cell for its driving, and an erase period for erasing wall charges within the discharged cell.
In the reset period, a rising ramp waveform Ramp-up is simultaneously applied to all the scan electrodes Y in a set-up interval. This rising ramp waveform Ramp-up causes a discharge within cells at the full field to generate wall charges within the cells. The setup discharge causes positive wall charges to be accumulated in the address electrode X and the sustain electrode Z, and negative wall charges to be accumulated in the scan electrode Y. In the set-down internal, after the rising ramp waveform was supplied, a falling ramp waveform Ramp-down, falling from a positive voltage lower than a peak voltage of the rising ramp waveform to a specific voltage level lower than the ground(GND) level voltage, causes a weak erasure discharge within the cells, to thereby erase excessive wall charges. The set-up discharge causes wall uniformly left within the cells of the full field to the extent that an address discharge may be performed stably.
In the address period, negative scan pulses SCAN are sequentially applied to the scan electrodes Y and at the same time positive data pulses DATA synchronized with the scan pulses SCAN are applied to the address electrodes X. When the voltage difference between the scan pulse SCAN and the data pulse DATA is added to the wall voltages generated in the reset period, the address discharge is generated within the cell to which the data pulse DATA is applied. When sustain voltages Vs are applied, wall charges to the extent that the discharge might be generated are formed within the cells selected by the address discharge. Positive DC voltage Vz is applied to the sustain electrode Z for the set-down interval and the address period so as not to generate a mis-discharge between the scan electrode Y and the sustain electrode Z.
In the sustain period, sustain pulses SUS are alternately applied to the scan electrodes Y and the sustain electrodes Z. In the cells selected by the address discharge, a sustain discharge, i.e., display discharge, is generated between the scan electrode Y and the sustain electrode Z whenever each sustain pulse SUS is applied as the wall voltage within the cell is added to the sustain pulse SUS.
Finally, after the sustain discharge has been finished, a voltage of an erasing ramp waveform Ramp-ers having a small pulse width is applied to the sustain electrode Z to thereby erase wall charges left within the cells of the full screen.
In the conventional driving method of a plasma display panel to which a driving waveform is adapted, the black brightness is relatively high upon driving, thus leading to a problem of deteriorating the contrast ratio of the panel.
Recently, the content or Xe tends to be increased in order to enhance discharge efficiency in the sealed discharge gas of the PDP. In this case, if a driving waveform according to the conventional driving method of the plasma display panel is adapted, the interference of the address electrode Y on a discharge between the scan electrode and the sustain electrode Z is increased to thus increase a reset voltage. Resultantly, in the event such a driving waveform is adapted to a large screen, there is a problem that the driving margin of the panel is deteriorated.
Moreover, there is a problem that if the content of Xe is increased, the address jitter characteristic is deteriorated, which makes a sustain discharge unstable in the subsequent period, i.e., a sustain period.